It is known in the medical field to utilize an implantable prosthesis to support a duct or vessel in a mammalian body. One such prosthesis may include a frame-like structure. Such frame-like structures are commonly known as a “stent”, “stent-graft” or “covered stent.” For the purpose of discussion, these structures are referred to collectively herein as a “stent.”
The stent can be utilized to support a duct or vessel in the mammalian body that suffers from an abnormal widening (e.g., an aneurysm, vessel contraction or lesion such as a stenosis or occlusion), or an abnormal narrowing (e.g., a stricture). Stents are also utilized widely in the urethra, esophagus, biliary tract, intestines, arteries, veins, as well as peripheral vessels. The stent can be delivered via a small incision on a host body. Hence, the use of stents as a minimally invasive surgical procedure has become widely accepted.
The stents can be cut from a tube or wound from a wire on a mandrel. Thereafter, the stents can be expanded in the duct or vessel of a host by a separate mechanism (e.g., balloon) or by utilization of a material that self-expands upon predetermined implantation conditions.
One common form of the stent is configured as a series of essentially identical rings connected together to form a lattice-like framework that defines a cylindrical or tubular framework. The series of rings may or may not have connecting linkages between the adjacent rings. One example does not utilize any connecting linkages between adjacent rings as it relies upon a direct connection from one ring to the next ring. It is believed that more popular examples utilize connecting linkages between adjacent rings, which can be seen in stent products offered by various companies in the marketplace.
All of the above stent examples utilize a biocompatible metal alloy (e.g., Nitinol or Elgiloy). The most common metal alloy utilized by these examples is Nitinol which has strong shape memory characteristics so that Nitinol self-expand when placed in the duct or vessel of a mammalian body at normal body temperature. In addition to self-expansion, these stents utilize a series of circular rings placed adjacent to each other to maintain an appropriate longitudinal spacing between each rings. These stents are also intended to be a permanent implant in that removal subsequent to implantation requires major invasive surgery.
Recently, however, stents are being investigated for use in a host as a temporary implant by having the stents degrade or absorbed by the host body. The primary advantage of such temporary stents is the elimination of additional surgery to remove the stent after it has served its function of dilating a lesion or stenosis in the vessel or duct. The entire stent is believed to be resorbed by the host body after a period of time after implantation.
More recently, a combination of the features of the permanent stent and the bio-resorbable stent are also known. For example, U.S. Patent Publication US2005/0222671 (published Oct. 6, 2005) shows and describes a series of connected annular rings with some of the connectors being biodegradable over time. U.S. Pat. No. 6,258,117 shows and describes at least a series of rings made from a biocompatible material (e.g., metal alloys) connected to each other via breakable or biodegradable links or connectors.
It is believed that these examples of partially biodegradable stents present a potential problem in that once the connecting linkages have biodegraded, the separated or unjoined annular rings could be susceptible to migration in the host body. It is believed that in a situation where the connector linkages have degraded faster than tissue incorporation (e.g., endothialization) of the annular rings, the rings could have the ability to migrate away from the original implantation site. Where the stent is a covered stent (i.e., a stent-graft), it is also believed that migration of discrete sections of the stent-graft could occur.
There is thus a need for an implantable prosthesis device that maintains the patency of a vessel with little or no ability to migrate from the implantation site while maintaining the patency of the duct or vessel of the host.